Lake Ontario water levels remain abnormally high

The International Lake Ontario–St. Lawrence River Board met Monday to determine whether it would keep the outflow from Lake Ontario at 10,000 cubic metres per second to address high water levels.

In a release sent out last Friday, the board said water levels downstream on the St. Lawrence River near Montreal remained at nearly the same high levels seen since early May. On June 1, Lake Ontario was 75.87 metres deep — 82 centimetres above its long-term average level for this time of year. The level at Lake St. Lawrence was about 28 centimetres above average, while the level at Lake St. Louis was about 22.49 metres, or 108 centimetres above average.

“Despite more heavy rain last week, the water level of Lake Ontario has remained relatively stable and continues to be within a couple of centimetres of its level two weeks ago,” the release said.

It said the current outflow is equivalent to the historic maximum weekly average outflow from Lake Ontario which occurred in just two weeks previously, once each during high water years of 1993 and 1998.

The board said it has been maximizing outflows from Lake Ontario in consideration of balancing water levels upstream and downstream, through Ontario and into Quebec along the St. Lawrence, to minimize flood and erosion impacts.

It is also considering options that would allow it to increase the outflow further, once downstream conditions permit. The outflow of Lake Ontario is controlled by 32 turbines at the Moses Saunders Dam between Cornwall, Ont., and Massena, N.Y.

Following the wet conditions in April and record rainfall during the first weeks of May, it has been generally drier across the Lake Ontario–St. Lawrence River basin. And if drier conditions continue, Lake Ontario outflows are expected to surpass inflows. Lake Ontario’s water level will begin to decline when that happens.

“However, owing to the huge surface area and large volume of water on Lake Ontario, it will take several weeks to significantly reduce levels, and longer to return to the average water level for the time of year.”

For a look at outflow changes, follow the board on Facebook at www.facebook.com/InternationalLakeOntarioStLawrenceRiverBoard.